Water-based drilling fluids that include lubricants

ABSTRACT

One or more embodiments presently described are directed to drilling fluid compositions that include lubricants, methods for making drilling fluids, and methods for drilling subterranean wells utilizing the drilling fluids. According to one embodiment, a drilling fluid composition may include a base fluid including water, a weighting agent in an amount of from 0.1 weight percent (wt. %) to 75 wt. % relative to the total weight of the water-based drilling fluid, and a lubricant in an amount of from 1 wt. % to 10 wt. % relative to the total weight of the water-based drilling fluid. The lubricant may include one or more alkyl esters and a fatty acid blend including at least palmitic acid and stearic acid. The sum of the weight percent of the palmitic acid and stearic acid may be at least 50 wt. % of the fatty acid blend.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to materials andmethods utilized in natural resource wells and, more specifically, tolubricants which may be used in drilling operations.

BACKGROUND

Drilling operations, for example, drilling a new wellbore forhydrocarbon extraction, may include the practice of continuouslycirculating a drilling fluid (alternatively known as a drilling mud)through the wellbore during the operation. The drilling fluid may bepumped into the drill pipe to the bottom of the borehole, where thedrilling fluid then flows upwardly through an annular space between thewellbore wall and the drill pipe and finally returns to the surface andflows out of the wellbore, where it may be recovered. During drilling,the drilling solids, such as portions of the drilled geologicalformation, may be carried by the drilling fluid from at or near thebottom of the wellbore to the surface. After its return to the surface,the drilling fluid may be mechanically or chemically treated to removecaptured solids and drill cuttings from the drilling fluid beforerecirculation back through the wellbore.

SUMMARY

Drilling fluids are used in various drilling applications, such asrotary drilling and coiled tube drilling applications, to completefunctional tasks and ensure that the drilling operation is safe andeconomical. One objective of a drilling fluid may be the reduction offriction between the drill string and the casing or the borehole wall byacting as a lubricating medium between the metal-metal interface and themetal-mudcake interface while drilling. Some conventional water-baseddrilling fluids may have poor lubricating properties and, thus, may havea much greater coefficient of friction compared to oil-based drillingfluid systems. This is one of the major technical limitations ofwater-based drilling fluid systems compared to oil-based drilling fluidsystems. To minimize the frictional resistance or coefficient offriction value of water-based drilling fluids, lubricating additives maybe incorporated in the drilling fluid systems. However, many of theseconventional materials have limitations in their applications. Some ofthe conventional lubricants have limited capacity to reduce thecoefficient of friction of drilling fluids in downhole operations, somelack the requisite thermal and chemical stability, and some are poorlybiodegradable, toxic, or not “ecologically-friendly” and, as such, haverestricted applications for ecologically sensitive environments. Someconventional lubricants have shown a lack of oxidative stability.Additionally, some conventional lubricants lack ability to reduce thecoefficient of friction of drilling fluids that comprise monovalent ordivalent salts. For example, many conventional lubricants have displayeda capacity to reduce the coefficient of friction of some drillingfluids, such as a bentonite mud, while being ineffective to reduce thecoefficient of friction of other drilling fluids, such as a KCl-Polymermud.

As such, there are ongoing needs for water-based drilling fluid systemswith lubricating additives that may, for example, reduce the coefficientof friction of a broad range of drilling fluids while minimizingnegative impact to the surrounding environment. One or more embodimentsof the present disclosure include water-based drilling fluid systemsthat include a lubricant that includes a fatty acid blend and an alkylester. The disclosed water-based drilling fluid systems with thelubricant have improved stability, improved lubrication properties, andecologically-friendly qualities when compared to water-based drillingfluids without lubricants and water-based drilling fluid systemsincorporating conventional lubricants.

According to one or more embodiments, a water-based drilling fluid maycomprise a base fluid comprising water, a weighting agent in an amountof from 0.1 weight percent (wt. %) to 75 wt. % relative to the totalweight of the water-based drilling fluid, and a lubricant in an amountof from 1 wt. % to 10 wt. % relative to the total weight of thewater-based drilling fluid. The lubricant may comprise one or more alkylesters and a fatty acid blend comprising at least palmitic acid andstearic acid. The sum of the weight percent of the palmitic acid andstearic acid may be at least 50 wt. % of the fatty acid blend.

According to another embodiment, a water-based drilling fluid may bemade by a method comprising mixing a base fluid, a weighting agent in anamount of from 0.1 wt. % to 75 wt. % relative to the total weight of thewater-based drilling fluid, and a lubricant in an amount of from 1 wt. %to 10 wt. % relative to the total weight of the water-based drillingfluid. The base fluid may comprise water. The lubricant may comprise oneor more alkyl esters and a fatty acid blend comprising at least palmiticacid and stearic acid. The sum of the weight percent of the palmiticacid and stearic acid may be at least 50 wt. % of the fatty acid blend.

According to yet another embodiment, a subterranean well may be drilledby a method comprising operating a drill in a wellbore in the presenceof the water-based drilling fluid. The water-based drilling fluid maycomprise a base fluid comprising water, a weighting agent in an amountof from 0.1 wt. % to 75 wt. % relative to the total weight of thewater-based drilling fluid, and a lubricant in an amount of from 1 wt. %to 10 wt. % relative to the total weight of the water-based drillingfluid. The lubricant may comprise one or more alkyl esters and a fattyacid blend comprising at least palmitic acid and stearic acid. The sumof the weight percent of the palmitic acid and stearic acid may be atleast 50 wt. % of the fatty acid blend.

Additional features and advantages of the described embodiments will beset forth in the detailed description which follows, and in part will bereadily apparent to those skilled in the art from that description orrecognized by practicing the described embodiments, including thedetailed description which follows and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of specific embodiments of thepresent disclosure can be best understood when read in conjunction withthe following drawing in which:

FIG. 1 depicts a flowchart of an example process of producing one ormore alkyl esters from a vegetable oil source, according to one or moreembodiments described in this disclosure.

Reference will now be made in greater detail to various embodiments,some embodiments of which are illustrated in the accompanying drawing.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to lubricants forwater-based drilling fluids and, additionally, to water-based drillingfluids incorporating the disclosed lubricants. The water-base drillingfluid may include at least a base fluid comprising water, a weightingagent in an amount of from 0.1 wt. % to 75 wt. % relative to the totalweight of the water-based drilling fluid, and a lubricant in an amountof from 1 wt. % to 10 wt. % relative to the total weight of thewater-based drilling fluid. The lubricant may include one or more alkylesters and a fatty acid blend comprising at least palmitic acid andstearic acid, where the sum of the weight percent of the palmitic acidand stearic acid is at least 50 wt. % of the fatty acid blend. Aspresently described, the fatty acid blend includes all fatty acids inthe lubricant, and sometimes all of the fatty acids in the drillingfluid into which the lubricant may be incorporated. Embodiments of thepresently disclosed water-based drilling fluid may be formulated toprovide improved lubricity. Specifically, the disclosed water-baseddrilling fluids may include lubricants that may be formulated tocomprise a fatty acid blend in addition to alkyl esters. Thisformulation may comprise, in one or more embodiments, the same or areduced coefficient of friction when compared to conventional lubricantssuitable for water-based drilling fluids, while also being suitable forwater-based drilling fluids that contain monovalent or divalent salts.

In one or more embodiments, the water-based drilling fluid may include abase fluid. The base fluid of the water-based drilling fluid may includewater. In one or more embodiments, the water includes one or more ofdeionized, tap, distilled, or fresh waters; natural, brackish, orsaturated salt waters; natural, salt dome, hydrocarbon formationproduced, or synthetic brines; filtered or untreated sea waters; mineralwaters; or potable and non-potable waters containing one or more ofdissolved salts, minerals, or organic materials. The base fluid of thewater-based drilling fluid may additionally include, for example, asalt. In one or more embodiments, the base fluid may include a saltbrine that includes water and a salt chosen from one or more of calciumchloride, calcium bromide, sodium chloride, sodium bromide, orcombinations of these. The water-based drilling fluid may include from25 wt. % to 99 wt. % base fluid, based on the total weight of thewater-based drilling fluid. In one or more embodiments, the water-baseddrilling fluid may include from 25 wt. % to 95 wt. %, from 25 wt. % to75 wt. %, from 25 wt. % to 50 wt. %, from 25 wt. % to 35 wt. %, from 35wt. % to 99 wt. %, from 35 wt. % to 95 wt. %, from 35 wt. % to 75 wt. %,from 35 wt. % to 50 wt. %, from 50 wt. % to 99 wt. %, from 50 wt. % to95 wt. %, from 50 wt. % to 75 wt. %, from 75 wt. % to 99 wt. %, from 75wt. % to 95 wt. %, or from 95 wt. % to 99 wt. % base fluid, such as oneor a mixture of any of the presently described water-based substances,based on the total weight of the water-based drilling fluid.

In one or more embodiments, the water-based drilling fluid may include aweighting agent. The weighting agent may increase the weight, thedensity, or both, of the water-based drilling fluid. Weighting agentsmay be used to control formation pressures, to help combat the effectsof sloughing or heaving shales that may be encountered in stressedareas, or a combination of these. Substances that are denser than waterand that do not generally have an adverse effect on other properties ofthe drilling fluid may be used as a weighting agent. In one or moreembodiments, the weighting agent may be a particulate solid having aspecific gravity of greater than 1, which may be sufficient to increasethe density of the drilling fluid composition by a certain amountwithout adding excessive mass such that the water-based drilling fluidcannot be efficiently circulated through the wellbore. The weightingagent may have a density of from 2 grams per cubic centimeter (g/cm³) to6 g/cm³. Examples of weighting agents include barite (BaSO₄), galena(PbS), hematite (Fe₂O₃), magnetite (Fe₃O₄), manufactured iron oxide,ilmenite (FeO.TiO₂), siderite (FeCO₃), celesite (SrSO₄), dolomite(CaCO₃.MgCO₃), and calcite (CaCO₃). These example weighting agents maybe used alone or in combination with one another.

In one or more embodiments, the water-based drilling fluid may includean amount of weighting agent sufficient to increase the density of thewater-based drilling fluid to allow the water-based drilling fluid tosupport the wellbore and prevent fluids in downhole formations fromflowing into the wellbore. The water-based drilling fluid may includefrom 0.1 wt. % to 75 wt. % weighting agent based on the total weight ofthe water-based drilling fluid. In one or more embodiments, thewater-based drilling fluid may include 0.1 wt. % to 60 wt. %, from 0.1wt. % to 50 wt. %, from 0.1 wt. % to 40 wt. %, from 0.1 wt. % to 30 wt.%, from 0.1 wt. % to 20 wt. %, from 0.1 wt. % to 10 wt. %, from 0.1 wt.% to 5 wt. %, from 0.1 wt. % to 1 wt. %, from 1 wt. % to 75 wt. %, from1 wt. % to 60 wt. %, from 1 wt. % to 50 wt. %, from 1 wt. % to 40 wt. %,from 1 wt. % to 30 wt. %, from 1 wt. % to 20 wt. %, from 1 wt. % to 10wt. %, from 1 wt. % to 5 wt. %, from 5 wt. % to 75 wt. %, from 5 wt. %to 60 wt. %, from 5 wt. % to 50 wt. %, from 5 wt. % to 40 wt. %, from 5wt. % to 30 wt. %, from 5 wt. % to 20 wt. %, from 5 wt. % to 10 wt. %,from 10 wt. % to 75 wt. %, from 10 wt. % to 60 wt. %, from 10 wt. % to50 wt. %, from 10 wt. % to 40 wt. %, from 10 wt. % to 30 wt. %, from 10wt. % to 20 wt. %, from 20 wt. % to 75 wt. %, from 20 wt. % to 60 wt. %,from 20 wt. % to 50 wt. %, from 20 wt. % to 40 wt. %, from 20 wt. % to30 wt. %, from 30 wt. % to 75 wt. %, from 30 wt. % to 60 wt. %, from 30wt. % to 50 wt. %, from 30 wt. % to 40 wt. %, from 40 wt. % to 75 wt. %,from 40 wt. % to 60 wt. %, from 40 wt. % to 50 wt. %, from 50 wt. % to75 wt. %, from 50 wt. % to 60 wt. %, or from 60 wt. % to 75 wt. %weighting agent based on the total weight of the water-based drillingfluid. In one or more embodiments, the weight ratio of the weightingagent to the base fluid may be from 10:100 to 300:100. For example, theweight ratio of the weighting agent to the base fluid may be from 10:100to 200:100, from 10:100 to 100:100, from 10:100 to 75:100, from 10:100to 50:100, from 10:100 to 25:100, from 25:100 to 300:100, from 25:100 to200:100, from 25:100 to 100:100, from 25:100 to 75:100, from 25:100 to50:100, from 50:100 to 300:100, from 50:100 to 200:100, from 50:100 to100:100, from 50:100 to 75:100, from 75:100 to 300:100, from 75:100 to200:100, from 75:100 to 100:100, from 100:100 to 300:100, from 100:100to 200:100, or from 200:100 to 300:100 depending on the desired densityof the final water-based drilling fluid.

In one or more embodiments, the water-based drilling fluid may include alubricant. Lubricants may be used to increase the lubricity of thewater-based drilling fluid, decrease friction between the drill stringand the wellbore during drilling operations, or both. A reduction in thecoefficient of friction of the water-based drilling fluid containing thelubricant may provide a reduction in friction experienced between thedrilling components and the wellbore, such as the drill string and thewellbore. The coefficient of friction may be measured in accordance witha standard lubricity coefficient test. A lubricity testing devicecommonly used by those in the drilling fluid industry (for example, OFITesting Equipment, Inc. (OFITE), Houston, Tex.) may be utilized formeasuring the coefficient of friction. The water-based drilling fluidmay comprise a coefficient of friction of from 0.01 to 0.10. In one ormore embodiments, the water-based drilling fluid may comprise acoefficient of friction of from 0.01 to 0.09, from 0.01 to 0.08, from0.01 to 0.07, from 0.01 to 0.06, from 0.01 to 0.05, from 0.01 to 0.04,from 0.01 to 0.03, from 0.01 to 0.02, from 0.02 to 0.10, from 0.03 to0.10, from 0.04 to 0.10, from 0.05 to 0.10, from 0.05 to 0.10, from 0.06to 0.10, from 0.07 to 0.10, from 0.08 to 0.10, or from 0.09 to 0.10.

In one or more embodiments, the lubricant may include at least one ormore alkyl esters. The alkyl esters may be derived from saturated freefatty acids, mono-unsaturated free fatty acids, polyunsaturated fattyacids, or combinations of these. It should be understand that “derivedfrom” may mean that the alkyl esters are those formed from thetransesterification of fatty acids in the presence of alcohols. In oneor more embodiments, the alkyl esters may be derived from fatty acidsthat include molecules from 16 carbon atoms to 20 carbon atoms. Forexample, the alkyl esters may be derived from fatty acids that includemolecules from 16 carbon atoms to 19 carbon atoms, from 16 carbon atomsto 18 carbon atoms, from 16 carbon atoms to 17 carbon atoms, from 17carbon atoms to 20 carbon atoms, from 18 carbon atoms to 20 carbonatoms, or from 19 carbon atoms to 20 carbon atoms. The alkyl esters maybe derived from fatty acids in the presence of a short chain alcohol. Inone or more embodiments, the alkyl esters may be derived from fattyacids in the presence of at least one or more of methanol, ethanol,propanol, butanol, or combinations of them.

Without being bound by theory, the alkyl esters may serve multiplefunctions in the lubricant. For example, the alkyl esters may improvethe total lubricating efficiency of the water-based drilling fluid byreducing the coefficient of friction of the water-based drilling fluid.The alkyl esters may also improve the pour point of the water-baseddrilling fluid comprising the lubricant and act as an effective carrierto transport the fatty acid blend, discussed subsequently, into theinterfaces of two mating surfaces present between the drillingcomponents. The alkyl esters may also create an adsorbed surface layeron the solid surfaces of the drilling components and facilitate thedistribution of the load exerted across the entire film to preventlocalized concentrations of stresses.

In one or more embodiments, the alkyl esters may include plant-basedalkyl esters derived from raw oil, such as a plant-based oil (forexample, vegetable oil). As presently described, “raw” oil refers to thepre-esterified oil which is utilized to form the alkyl esters. Dependingon the source of plants or seeds used to produce the vegetable oil, avegetable oil may contain a mixture of different types of free fattyacids such as saturated, mono unsaturated, poly unsaturated, omega 3,omega 6, or omega 9 free fatty acids. When vegetable oil undergoestransesterification in the presence of short chain alcohols (such asmethanol, ethanol, propanol, and butanol), the resulting alkyl estersare derived from the free fatty acids present in the triglycerides ofthe vegetable oil. In one or more embodiments, the alkyl esters may bederived from vegetable oils that may be commonly used in foodpreparation. Commonly used vegetable oils that may be used in foodpreparation include, but are not limited to, olive oil, palm oil,sunflower oil, corn oil and peanut oil.

A vegetable oil, such as that used in forming the alkyl esters, may be“fresh” or “waste” vegetable oil. In one or more embodiments, theplant-based alkyl esters may be derived from a fresh vegetable oil.“Fresh” vegetable oils, which may also be referred to as “pure vegetableoils,” have not been processed or used in food preparation. In one ormore embodiments, the plant-based alkyl esters may be derived from awaste vegetable oil. “Waste” vegetable oils, which may also be referredto as “used” vegetable oils, include previously fresh vegetable oilsthat have been used in food preparation or similarly processed. Wastevegetable oils may also be referred to as “recycled” vegetable oil whenthe waste vegetable oil is then further processed or used in some way.Waste vegetable oils may be used as a sustainable, inexpensive source ofvegetable oil. In one or more embodiments, the water-based drillingfluid that includes the plant-based alkyl esters derived from vegetableoil may have a reduced coefficient of friction when compared toconventional water-based drilling fluids. Such water-based drillingfluids may also be environmentally-friendly as they are derived fromnaturally occurring oils.

In one or more embodiments, the alkyl esters may be derived from a rawoil that has a plastic viscosity of at least 50 centipoise (cP), or evenat least 60.8 cP, measured using a multi-speed rotational viscometer. Insome embodiments, the plastic viscosity of the raw oil to the viscosityof mineral oil (referred to as “the plastic viscosity ratio”) may be atleast 10. For example, the plastic viscosity ratio may be 11.18.

In one or more embodiments, the lubricant may include from 50 wt. % to75 wt. % of alkyl esters based on the total weight of the lubricant. Forexample, the lubricant may include from 55 wt. % to 75 wt. %, from 60wt. % to 75 wt. %, from 65 wt. % to 75 wt. %, from 70 wt. % to 75 wt. %,from 50 wt. % to 70 wt. %, from 50 wt. % to 65 wt. %, from 50 wt. % to60 wt. %, or from 50 wt. % to 55 wt. % of alkyl esters based on thetotal weight of the lubricant.

Now referring to FIG. 1, a flowchart of an example process 100 ofproducing the presently described alkyl esters is depicted. In step 102,the raw material oil that includes fatty acids, such as vegetable oil,is obtained. In some implementations, the raw oil can be processed orwaste vegetable oil produced as a byproduct by the food industry asdescribed previously in this disclosure. Alternatively, the raw materialoil can be pure vegetable oil.

In step 104, impurities are removed from the raw material oil. Theimpurities, such as food residues, can reduce the functional capabilityof the raw material oil. In one or more embodiments, the raw materialoil can be filtered at a decreased pressure. In one or more embodiments,the raw material oil can be filtered at a pressure range of 5 pounds persquare inch (PSI) to 10 PSI. For example, a reduced pressure filtrationcell may be used to remove impurities, such as burnt and unburned foodresidue, which may be present in the waste vegetable oil. The reducedpressure filtration cell may include filter paper with pore sizes thatare less than 5 microns in order to remove impurities that are largerthan 5 microns. A constant pressure of 5 PSI to 10 PSI may be used onthe reduced pressure cell for quick filtration of a volume of the wastevegetable oil. In one or more embodiments, impurities may be removedfrom the raw material oil using alternative or additional methods. Forexample, filtration media or adsorbents that are capable of removingimpurities and excess water from waste vegetable oil can be used asalternatives or in addition to the reduced pressure filtration cell. Forexample, a multi-cell filtration apparatus can be used for removing theimpurities.

In step 106, the raw material waste oil is esterified. In one or moreembodiments, the raw material waste oil is esterified in the presence ofa catalyst to produce alkyl ester products and triglycerides. In one ormore embodiments, the catalyst may include at least one of sodiumhydroxide, potassium hydroxide, sodium alkoxide, potassium alkoxide, orcombinations of these. For example, the raw material oil can beesterified with methanol in the presence of sodium hydroxide. To do so,a volume of methanol (such as 20 volumetric percent of the originalwaste vegetable oil volume) and a mass of NaOH (such as 4.22 grams (g)NaOH per liter of waste vegetable oil) may be mixed in a dry conditionusing a magnetic stirrer and then added to the waste vegetable oil in acontainer. The mixture may then be stirred for six hours using themagnetic stirrer to complete the interactions. The quantity of catalystrequired to process the waste vegetable oil may be determined bytitration method. To do so, 1 milliliter (mL) of waste vegetable oil maybe mixed with 10 mL of isopropyl alcohol of 99.2% purity. To thismixture, 2-3 drops of an indicator fluid, such as phenolphthalein, maybe added. The indicator fluid is added drop by drop into the agitatedwaste vegetable oil until the color changes to pink. After the endpoint,the mixture is stirred to check the permanency of the pink color. Thetitration test is repeated three times to calculate the average amountof catalyst required to reach the endpoint. After determining theaverage value of sodium hydroxide (NaOH) based on the titration testresults, a constant value of 3.5 g is added to determine the totalamount of catalyst (for example, between 4.18 g and 4.22 g) required for1 liter of waste vegetable oil.

In step 108, the alkyl ester products and triglycerides are separated.In some embodiments, the total reaction product from 106 may be allowedto stay in static conditions overnight to complete the sedimentation ofglycerol and sludge at the bottom of the container. During the initialsettling phase, if some emulsion were formed, for example, due to thepresence of some emulsion forming byproducts in the ester layer, theemulsion can be broken by heating the processed mass at approximately80° C. or adding approximately 10 mL of acetic acid per liter of wastevegetable oil to break and prevent the emulsion formation. In someembodiments, the esterified oil and the washed water may be kept instatic condition overnight for effective separation of oil and waterphases.

In step 110, the alkyl ester products are washed. After completesedimentation at 108, the top clear esterified oil may be decantedslowly and washed for several hours using water while stirring with amagnetic stirrer. The separated oil phase may be decanted slowly toremove it from the water phase. In some embodiments, the process ofwashing may be repeated two or more times.

In step 112, alkyl ester products are heated to remove any residualwater and the short chain alcohol. In some embodiments, after the finalwashing of 110, the washed, esterified oil may be heated to 80° C. underdynamic condition using a hot plate and a magnetic stirrer. This mayremove water and methanol from the processed vegetable oil resulting inthe washed and heated alkyl ester products substantially free ofresidual water and short chain alcohol included in esterified rawmaterial oil. As used in this disclosure, the term “substantially free”of a component means less than 1 wt. % of that component in a particularportion of a product. As an example, the alkyl ester products, which maybe substantially free of residual water and short chain alcohol includedin esterified raw material oil, may have less than 1 wt. % of water andless than 1 wt. % of short chain alcohol. Implementing the previouslydescribed steps of process 100 produces washed and heated alkyl esterproducts that are substantially (in one or more embodiments, entirely)free of residual water, short chain alcohol, or both that may be presentin esterified raw material oil. The washed and heated alkyl esterproducts are void of triglycerides that may be present in the esterifiedraw material oil.

In one or more embodiments, the lubricant also includes a fatty acidblend. The fatty acid blend may include at least palmitic acid andstearic acid. The sum of the weight percent of the palmitic acid and thestearic acid may be at least 50 wt. % of the fatty acid blend. In one ormore embodiments, the sum of the weight percent of the palmitic acid andstearic acid may be from 50 wt. % to 99 wt. %, from 55 wt. % to 99 wt.%, from 60 wt. % to 99 wt. %, from 65 wt. % to 99 wt. %, from 70 wt. %to 99 wt. %, from 75 wt. % to 99 wt. %, from 80 wt. % to 99 wt. %, from85 wt. % to 99 wt. %, from 90 wt. % to 99 wt. %, from 95 wt. % to 99 wt.%, from 50 wt. % to 95 wt. %, from 50 wt. % to 90 wt. %, from 50 wt. %to 85 wt. %, from 50 wt. % to 80 wt. %, from 50 wt. % to 75 wt. %, from50 wt. % to 70 wt. %, from 50 wt. % to 65 wt. %, from 50 wt. % to 60 wt.%, or from 50 wt. % to 55 wt. % of the fatty acid blend. The fatty acidblend may include palmitic acid and stearic acid, in some embodiments,in a molar ratio of from 20:80 to 40:60. In one or more embodiments, thefatty acid blend may include palmitic acid and stearic acid in a molarratio of from 21:79 to 35:65, from 22:78 to 34:66, from 23:77 to 33:67,from 24:76 to 32:68, from 25:75 to 31:69, from 23:74 to 30:70, or from27:73 to 29:71. The fatty acid blend may also include any fatty acidthat does not adversely affect other properties of the lubricant. Forexample, the structure of a fatty acid, such as the length of the carbonchain, may result in differences in physical properties of the lubricantsuch as melting point and pour point. Fatty acids which may precipitateat lower temperatures may not be suitable for use in the lubricant.

The fatty acid blend may serve a number of functions in the lubricant.The fatty acid blend may enhance the lubricant's capacity to reduce thecoefficient of friction of the water-based drilling fluid. When thefatty acid blend is homogenously dispersed within the alkyl estermixture, described previously in this disclosure, it may improve theinterface penetration capacity of the lubricant to create a thin butstrong lubricating film on the surfaces of the drilling components. Thefatty acid blend may also increase the oxidative stability of the alkylesters, preventing a loss of lubricating capacity when the water-baseddrilling fluid comprising the lubricant includes a monovalent ordivalent salt.

The lubricant may include from 25 wt. % to 50 wt. % of the fatty acidblend based on the total weight of the lubricant. In one or moreembodiments, the lubricant may include from 30 wt. % to 50 wt. %, from35 wt. % to 50 wt. %, from 40 wt. % to 50 wt. %, from 45 wt. % to 50 wt.%, from 25 wt. % to 45 wt. %, from 25 wt. % to 40 wt. %, from 25 wt. %to 35 wt. %, or from 25 wt. % to 30 wt. % of the fatty acid blend basedon the total weight of the lubricant.

The fatty acid may be a liquid and, in some embodiments, the lubricantmay be a homogenous mixture free of solids. Solids may have the tendencyto undesirably form in a lubricant including fatty acids upon additionto a water-based drilling fluid. The formation of these solids may beattributed to the inability of fatty acid to uniformly distribute in thelubricant, causing a non-homogeneous lubricant and, as a result, anon-homogenous drilling fluid. The formation of solids in the drillingfluid alters the homogeneity of the lubricant, and homogeneity may bebeneficial or outright required in a lubricant. Therefore, if thelubricant contains these solids, it may not be an acceptable form of alubricant.

In one or more embodiments, the weight ratio of the one or more alkylesters to the fatty acid blend may be from 1:1 to 3:1. For example, theweight ratio of the one or more alkyl esters to the fatty acid blend maybe from 1:1 to 2.5:1, from 1:1 to 2:1, from 1:1 to 1.5:1, from 1.5: to2:1, from 1.5:1 to 2.5:1, from 1.5:1 to 3:1, or from 2:1 to 3:1. Such aweight ratio may ensure that the fatty acid blend remains uniformlydistributed within the alkyl esters and prevent precipitation. Such aweight ratio may also ensure the liquid state of the lubricant at bothwarm and cold temperatures and may prevent any separation andprecipitation of the fatty acid blend at colder temperatures, such asthose present at an ocean bottom or the surface of a well located in acolder region.

In one or more embodiments, the water-based drilling fluid may includean amount of lubricant sufficient to decrease the coefficient offriction of the water-based drilling fluid to allow the water-baseddrilling fluid to produce a lubricating film in the interface of twometallic surfaces or a metallic surface and a non-metallic surface, suchas the drill pipe and the borehole wall. In one or more embodiments, thedecrease of the coefficient of friction mitigates the torque and dragproblems encountered in horizontal or extended-reach well drillingapplications. A horizontal well is a well with an inclination ofgenerally greater than 85 degrees (°) from true vertical. Horizontalwells are drilled to enhance reservoir performance by placing a longwellbore section within the reservoir. An extended-reach well is one inwhich the ratio of the measured depth versus the true vertical depth isat least 2:1. In case of horizontal and extended-reach wells, anincreased coefficient of friction can cause a reduction in drillingefficiency, an increase in equipment wear and pipe twist-off, areduction in the rate of penetration, an increase in the torque anddrag, or combinations of these, which can lead to various other drillingproblems. An increased coefficient of friction can also limit the reachof horizontal and extended-reach wells, causing a potential barrier fordrilling operations.

The water-based drilling fluid may include from 1 wt. % to 10 wt. %lubricant, based on the total weight of the water-based drilling fluid.In one or more embodiments, the water-based drilling fluid may includefrom 1 wt. % to 9 wt. %, from 1 wt. % to 7.5 wt. %, from 1 wt. % to 6wt. %, from 1 wt. % to 5 wt. %, from 1 wt. % to 4 wt. %, from 1 wt. % to3 wt. %, from 1 wt. % to 2 wt. %, from 2 wt. % to 10 wt. %, from 3 wt. %to 10 wt. %, from 4 wt. % to 10 wt. %, from 5 wt. % to 10 wt. %, from 6wt. % to 10 wt. %, from 7 wt. % to 10 wt. %, from 8 wt. % to 10 wt. %,or from 9 wt. % to 10 wt. % lubricant, based on the total weight of thewater-based drilling fluid. The weight ratio of the lubricant to thebase fluid may be from 1:100 to 10:100. In one or more embodiments, theweight ratio of the lubricant to the base fluid may be from 2:100 to10:100 , from 3:100 to 10:100, from 4:100 to 10:100, from 5:100 to10:100, from 6:100 to 10:100, from 7:100 to 10:100, from 8:100 to10:100, from 9:100 to 10:100, from 1:100 to 9:100, from 1:100 to 8:100,from 1:100 to 7:100, from 1:100 to 6:100, from 1:100 to 5:100, from1:100 to 4:100, from 1:100 to 3:100, or from 1:100 to 2:100.

In one or more embodiments, the water-based drilling fluid mayoptionally include one salts selected from monovalent salts, divalentsalts, or combinations of these. These salts may be in addition to thosepresent in the base fluid of the water-based drilling fluid, such assalt from salt water. Contemplated monovalent salts include, but are notlimited to, sodium chloride (NaCl), potassium chloride (KCl), potassiumacetate, potassium carbonate, potassium lignite, and potassium salt ofpartially-hydrolyzed polyacrylamide (PHPA). The divalent salts mayinclude, but are not limited to, calcium chloride (CaCl₂). Water-baseddrilling fluids which contain monovalent or divalent salts, such as KCl,may be used when drilling water-sensitive shales, such as hard, brittleshales. The ions, such as potassium ions (K⁺), may attach to claysurfaces and lend stability to shale exposed to drilling fluids. Theions may also assist in holding the cuttings together and minimize theirdispersion into finer particles. As clay surfaces are exposed topotassium ions, different ions, such as sodium and calcium ions, mayaccumulate and decrease the effectiveness of the drilling fluid.Further, some drilling fluid additives, such as the bentonitesubsequently discussed in this disclosure, may have a strong affinityfor certain ions and the use of such additives may be limited.

The water-based drilling fluid may include from 0.01 wt. % to 10 wt. %of one or a plurality of salts based on the total weight of thewater-based drilling fluid. For example, the water-based drilling fluidmay include from 1 wt. % to 10 wt. %, from 2 wt. % to 10 wt. %, from 3wt. % to 10 wt. %, from 4 wt. % to 10 wt. %, from 5 wt. % to 10 wt. %,from 6 wt. % to 10 wt. %, from 7 wt. % to 10 wt. %, from 8 wt. % to 10wt. %, from 9 wt. % to 10 wt. %, from 0.01 wt. % to 9 wt. %, from 0.01wt. % to 8 wt. %, from 0.01 wt. % to 7 wt. %, from 0.01 wt. % to 6 wt.%, from 0.01 wt. % to 5 wt. %, from 0.01 wt. % to 4 wt. %, from 0.01 wt.% to 3 wt. %, from 0.01 wt. % to 2 wt. %, or from 0.01 wt. % to 1 wt. %of one or a plurality of salts based on the total weight of thewater-based drilling fluid. In one or more embodiments. The weight ratioof the one or a plurality of salts to the base fluid may be from 1:100to 10:100. For example, the weight ratio of the one or a plurality ofsalts to the base fluid may be from 2:100 to 10:100, from 3:100 to10:100, from 4:100 to 10:100, from 5:100 to 10:100, from 6:100 to10:100, from 7:100 to 10:100, from 8:100 to 10:100, from 9:100 to10:100, from 1:100 to 9:100, from 1:100 to 8:100, from 1:100 to 7:100,from 1:100 to 6:100, from 1:100 to 5:100, from 1:100 to 4:100, from1:100 to 3:100, or from 1:100 to 2:100.

In one or more embodiments, the water-based drilling fluid mayoptionally include one or a plurality of additives to enhance theproperties and characteristics of the water-based drilling fluid system.The additives may include, but are not limited to, emulsifiers,fluid-loss control additives, viscosifiers (viscosity control agents),alkali compounds, friction reducers, or combinations of these. Thewater-based drilling fluid may also optionally include pH buffers,electrolytes, glycols, glycerols, dispersion aids, corrosion inhibitors,and defoamers.

In one or more embodiments, the water-based drilling fluid system mayoptionally include a viscosifier to impart non-Newtonian fluid rheologyto the water-based drilling fluid system to facilitate the lifting andconveying of rock cuttings to the surface of the wellbore. According toone or more embodiments, viscosifiers may include, but are not limitedto, xanthan gum polymer (XC polymer), bentonite, polyacrylamide,polyanionic cellulose, low-viscosity polyanionic cellulose (PAC-LV), orcombinations of these. In additional embodiments, the water-baseddrilling fluid system may optionally include a friction reducingmaterial, such as a finely ground altered calcium montmorillonite clay,commonly known as “rev dust.” In further embodiments, the water-baseddrilling fluid system may optionally include sodium asphalt sulfonate,commercially available as SOLTEX from Chevron Phillips Chemical Company.In one or more embodiments, the water-based drilling fluid may includefrom 0 wt. % to 2 wt. % of additives based on the total weight of thewater-based drilling fluid. For example, the water-based drilling fluidmay include from 0.5 wt. % to 2 wt. %, from 0.5 wt. % to 1.5 wt. %, from0.5 wt. % to 1 wt. %, from 1 wt. % to 2 wt. %, from 1 wt. % to 1.5 wt.%, or from 1.5 wt. % to 2 wt. % of additives based on the total weightof the water-based drilling fluid. The weight ratio of the additives tothe base fluid may be from 0.01:100 to 1:100. In one or moreembodiments, the weight ratio of the additives to the base fluid may befrom 0.05:100 to 1:100, from 0.1:100 to 1:100, from 0.25:100 to 1:100,from 0.5:100 to 1:100, from 0. 6:100 to 1:100, from 0. 7:100 to 1:100,from 0.8:100 to 1:100, from 0.9:100 to 1:100, from 0.01:100 to 0.9:100,from 0.01:100 to 0.8:100, from 0.01:100 to 0.7:100, from 0.01:100 to0.6:100, from 0.01:100 to 0.5:100, from 0.01:100 to 0.25:100, from0.01:100 to 0.1:100, or from 0.01:100 to 0.05:100.

In one or more embodiments, the water-based drilling fluid mayoptionally include at least one alkalinity adjuster. In one or moreembodiments, the water-based drilling fluid may optionally include atleast one alkaline compound to adjust the pH of the water-based drillingfluid. Examples of alkaline compounds may include, but are not limitedto, lime (calcium hydroxide or calcium oxide), soda ash (sodiumcarbonate), sodium hydroxide, potassium hydroxide, strong bases, orcombinations of these alkaline compounds. It is noted that conjugatebases to acids with an acid dissociation constant (pK_(a)) of more thanabout 13 are considered strong bases. The alkaline compounds may reactwith gases, such as CO₂ or H₂S, encountered by the drilling fluidcomposition during drilling operations to prevent the gases fromhydrolyzing components of the water-based drilling fluid. Thewater-based drilling fluid may optionally include from 0.1 wt. % to 1wt. % of alkalinity adjusters based on the total weight of thewater-based drilling fluid. In one or more embodiments, the water-baseddrilling fluid may include from 0.1 wt. % to 0.8 wt. %, from 0.1 wt. %to 0.6 wt. %, from 0.1 wt. % to 0.4 wt. %, from 0.1 wt. % to 0.2 wt. %,from 0.2 wt. % to 1 wt. %, from 0.2 wt. % to 0.8 wt. %, from 0.2 wt. %to 0.6 wt. %, from 0.2 wt. % to 0.4 wt. %, from 0.4 wt. % to 1 wt. %,from 0.4 wt. % to 0.8 wt. %, from 0.4 wt. % to 0.6 wt. %, from 0.6 wt. %to 1 wt. %, from 0.6 wt. % to 0.8 wt. %, or from 0.8 wt. % to 1 wt. % ofalkalinity adjusters based on the total weight of the water-baseddrilling fluid. The weight ratio of the alkalinity adjuster to the basefluid may be from 0.01:100 to 1:100. In one or more embodiments, theweight ratio of the alkalinity adjuster to the base fluid may be from0.05:100 to 1:100, from 0.1:100 to 1:100, from 0.25:100 to 1:100, from0.5:100 to 1:100, from 0. 6:100 to 1:100, from 0. 7:100 to 1:100, from0.8:100 to 1:100, from 0.9:100 to 1:100, from 0.01:100 to 0.9:100, from0.01:100 to 0.8:100, from 0.01:100 to 0.7:100, from 0.01:100 to 0.6:100,from 0.01:100 to 0.5:100, from 0.01:100 to 0.25:100, from 0.01:100 to0.1:100, or from 0.01:100 to 0.05:100.

In one or more embodiments, the water-based drilling fluid mayoptionally include at least one solid-phase component. Solid-phasecomponents in the water-based drilling fluid may include, but are notlimited to, the weighting agent, starch, soda ash, bentonite, lime,sodium sulfite, or combinations of these. As presently described, all ofthe solid-phase components together make up a total solids content ofthe water-based drilling fluid system. The water-based drilling fluidmay have a total solids content of less than or equal to 75 wt. % basedon the total weight of the water-based drilling fluid composition. Inadditional embodiments, the water-based drilling fluid may have a solidscontent of less than or equal to 50 wt. %, less than or equal to 25 wt.%, or less than or equal to 10 wt. % based on the total weight of thewater-based drilling fluid.

In one or more embodiments, fluid-loss control agents may be added tothe water-based drilling fluid to reduce the amount of filtrate lostfrom the water-based drilling fluid composition into a subsurfaceformation. Examples of fluid-loss control agents include organophilic(for example, amine-treated) lignite, bentonite, manufactured polymers,and thinners or deflocculants. When fluid-loss control agents are used,they may comprise from 0.5 wt. % to 3 wt. % of the water-based drillingfluid composition based on the total weight of the water-based drillingfluid. In one or more embodiments, fluid-loss control agents maycomprise from 0.5 wt. % to 1.25 wt. %, from 0.75 wt. % to 2 wt. %, from0.75 wt. % to 1.5 wt. %, from 0.75 wt. % to 1.25 wt. %, from 1 wt. % to2 wt. %, from 1 wt. % to 1.5 wt. %, or from 1 wt. % to 1.25 wt. % of thewater-based drilling fluid based on the total weight of the water-baseddrilling fluid. The weight ratio of the fluid-loss control agent to thebase fluid may be from 0.01:100 to 1:100. In one or more embodiments,the weight ratio of the fluid-loss control agent to the base fluid maybe from 0.05:100 to 1:100, from 0.1:100 to 1:100, from 0.25:100 to1:100, from 0.5:100 to 1:100, from 0.6:100 to 1:100, from 0.7:100 to1:100, from 0.8:100 to 1:100, from 0.9:100 to 1:100, from 0.01:100 to0.9:100, from 0.01:100 to 0.8:100, from 0.01:100 to 0.7:100, from0.01:100 to 0.6:100, from 0.01:100 to 0.5:100, from 0.01:100 to0.25:100, from 0.01:100 to 0.1:100, or from 0.01:100 to 0.05:100.

Having previously described the water-based drilling fluid and lubricantaccording to various embodiments, illustrative methods for preparing thedisclosed lubricant will now be described. The methods for preparing thelubricant may include mixing solid palmitic acid and solid stearic acidto make a solid fatty acid blend, heating the solid fatty acid blend toform a liquid fatty acid blend, mixing the liquid fatty acid blend withone or more alkyl esters to form a lubricant precursor, heating thelubricant precursor to a temperature of at least 50° C., andmechanically agitating the lubricant precursor while heating to form thedrilling fluid lubricant. The heating and mechanical agitation of thelubricant precursor may aid the lubricant to be a homogenous mixturesubstantially free from solids. As such, the lubricant may include lessthan 1 wt. % of solids. The heating and mechanical agitation may allowthe fatty acid blend to be uniformly distributed within the one or morealkyl esters. This uniform distribution may ensure that the fatty acidblend does not precipitate out of solution upon addition of thelubricant to the water-based drilling fluid. The uniform distributionmay also allow the lubricant to provide the benefits previouslydiscussed. In one or more embodiments, the fatty acid blend may beprovided as previously described in this disclosure with regard toembodiments of the water-based drilling fluid. In one or moreembodiments, the alkyl esters may be provided as previously described inthis disclosure with regard to embodiments of the water-based drillingfluid. In one or more embodiments, the solid fatty acid blend may beheated to a temperature sufficient to ensure the entire blend is in aliquid state. For example, in one or more embodiments the solid fattyacid blend may be heated to a temperature of from 40° C. to 60° C., from45° C. to 60° C., from 50° C. to 60° C., from 40° C. to 55° C., from 40°C. to 50° C., or from 40° C. to 45° C.

Having previously described the water-based drilling fluid according tovarious embodiments, illustrative methods for preparing the water-baseddrilling fluid will now be described. The methods for preparing thewater-based drilling fluid may include mixing a base fluid, a weightingagent, and a lubricant in an amount of from 1 wt. % to 10 wt. % relativeto the total weight of the water-based drilling fluid. In one or moreembodiments, the mixing step may optionally include adding at least onesalt selected from a monovalent salt, a divalent salt, or combinationsof these. In additional embodiments, the mixing step may optionallyinclude adding at least one additive such as an alkalinity adjuster,solid-phase component, fluid-loss control agent, or combinations ofthese. In one or more embodiments, the salt may be provided aspreviously described with regard to embodiments of the water-baseddrilling fluid. In one or more embodiments, the fatty acid blend may beprovided as previously described. In one or more embodiments, the alkylesters may be provided as previously described. In one or moreembodiments, the additives, alkalinity adjusters, solid-phasecomponents, or fluid-loss control agents may be provided as previouslydescribed with regard to embodiments of the water-based drilling fluid.

The water-based drilling fluid of the present disclosure may bewell-suited for use in drilling operations in subterranean formations.The water-based drilling fluid of the present disclosure may providelubrication functionality for cooling and lubricating the bit and drillstring in boring operations. Further, the lubricant of the presentdisclosure may impart enhanced lubricity to the water-based drillingfluid thereby providing increased lubrication and reduced frictionbetween the drill string, pipe, and wellbore during drilling operations.Accordingly, embodiments of methods for drilling in a subterranean wellmay include providing a water-based drilling fluid composition accordingto any embodiments described previously. The method for drilling in asubterranean well may comprise operating a drill in a wellbore in thepresence of the water-based drilling fluid. According to one or moreembodiments, to drill a subterranean well, a drill string, including adrill bit and drill collars to weight the drill bit, may be insertedinto a predrilled hole and rotated to cause the drill bit to cut intothe rock at the bottom of the hole. The drilling operation produces rockfragments. To remove the rock fragments from the bottom of the wellbore,a drilling fluid, such as the water-based drilling fluids presentlydescribed, may be pumped down through the drill string to the drill bit.The drilling fluid cools the drill bit, provides lubrication, and liftsthe rock fragments known as cuttings away from the drill bit. Thedrilling fluid carries the cuttings upwards as the drilling fluid isre-circulated back to the surface. At the surface, the cuttings areremoved from the drilling fluid through a secondary operation, and thedrilling fluid may be re-circulated back down the drill string to thebottom of the wellbore for collection of further cuttings.

Drilling fluids may serve a number of functions, with different types ofdrilling fluids specializing in particular functions. In one or moreembodiments, the water-based drilling fluid suspends the cuttings andthe weighting agent aids in transporting the cuttings to the wellboresurface with the water-based drilling fluid. Additionally, thewater-based drilling fluid may absorb gases in the wellbore, such ascarbon dioxide (CO₂), hydrogen sulfide (H₂S), and methane (CH₄), andtransport them to the wellbore surface for release, sequestration, orburn-off. The water-based drilling fluid may additionally providebuoyancy to the drill string, relieving the tension on the drill stringas the length of the wellbore increases. In one or more embodiments, thewater-based drilling fluid also provides a cooling and lubricationfunctionality for cooling and lubrication of the bit and drill stringutilized in boring operations. In additional embodiments, thewater-based drilling fluid may also aid in controlling subsurfacepressures. Specifically, the water-based drilling fluid may providehydrostatic pressure in the wellbore to provide support to the sidewallsof the wellbore and prevent the sidewalls from collapsing and caving inon the drill string. Additionally, the water-based drilling fluid mayprovide hydrostatic pressure in the bore to prevent fluids in thedownhole formations from flowing into the wellbore during drillingoperations.

EXAMPLES

The following examples illustrate one or more additional features of thepresent disclosure. It should be understood that these examples are notintended to limit the scope of the disclosure or the appended claims inany manner.

Example 1 Production of Sample Drilling Fluid Compositions (WithoutAdded Lubricant)

To compare the lubricating effect of the lubricant alone and in thepresence of a monovalent or divalent salt, four water-based drillingfluids were prepared. The formulation of each water-based drilling fluidis provided in Table 1 and described in the following correspondingparagraphs.

The first water-based drilling fluid, Drilling Fluid 1, was a bentonitemud that did not contain any monovalent or divalent salts. DrillingFluid 1 was prepared by mixing 340 mL of water, 0.25 g of soda ash, and25 g of bentonite.

The second water-based drilling fluid, Drilling Fluid 2, was aKCl-polymer mud that contained monovalent KCl salt. Drilling Fluid 2 wasprepared by mixing 335 mL of water, 0.25 g of soda ash, 5 g ofbentonite, 3 g of PAC-LV, 1 g of XC polymer, and 20 g of KCl.

The third water-based drilling fluid, Drilling Fluid 3, was a low-solid,non-dispersed (LSND) mud that contained monovalent KCl salt. DrillingFluid 3 was prepared by mixing 332 mL of water, 0.3 g of soda ash, 6 gof bentonite, 3 g of PAC-LV, 1 g of XC polymer, 20 g of KCl, 3 g ofSoltex, and 1 g of sodium sulfite.

The fourth water-based drilling fluid, Drilling Fluid 4, was a divalentsalt and rev dust contaminated KCl-polymer mud that contained bothmonovalent KCl salt and divalent CaCl₂ salt. Drilling Fluid 4 wasprepared by mixing 335 mL of water, 0.25 g of soda ash, and 5 g ofbentonite, 3 g of PAC-LV, 1 g of XC polymer, 20 g of KCl, 25 g of revdust, and 20 g of CaCl₂.

TABLE 1 Formulation of Water-Based Drilling Fluid Examples DrillingDrilling Drilling Drilling Component Fluid 1 Fluid 2 Fluid 3 Fluid 4Water (mL) 340 335 332 335 Soda Ash (g) 0.25 0.25 0.30 0.25 Bentonite(g) 25 5 6 5 PAC LV (g) 0 3 3 3 XC Polymer (g) 0 1 1 1 KCl (g) 0 20 2020 REV Dust (g) 0 0 0 25 CaCl₂ (g) 0 0 0 20 Soltex (g) 0 0 3 0 Sodium 00 1 0 Sulfite (g) pH 9.5 9.5 9.5 9.5

Drilling Fluids 1-4 were then tested for baseline coefficient offriction values without added lubricant as determined by a lubricitytester, commercially available as EP and Lubricity Tester from OFITE, byloading a portion of each drilling fluid into the lubricity tester andsubjecting a test block to 150 inch-pounds of torque within the samplefor 5 minutes. The results for each of these drilling fluids areprovided in Table 2.

TABLE 2 Coefficient of Friction (COF) Values of Drilling Fluids 1-4Sample Lubricant Drilling Fluid COF A1 None Drilling Fluid 1 0.48 A2None Drilling Fluid 2 0.38 A3 None Drilling Fluid 3 0.20 A4 NoneDrilling Fluid 4 0.39

Example 2 Production of Alkyl Esters

To prepare the alkyl esters, the source of waste vegetable used wasvegetable and cooking oil from restaurants. The waste vegetable oil wasa mixture of used vegetable oils, which included, but was not limitedto, corn oil, sunflower oil, palm oil, canola oil, and peanut oil.

The food and other contents present in the waste vegetable oil were thenfiltered off to remove the impurities from the raw material waste oiland a filtered raw material oil was produced. This filtering off stepwas performed by a low pressure filtration cell which removed impuritiesincluding burnt and unburned food residue that were present in the wastevegetable oil. The low pressure filtration cell utilized size 5micrometer (μm) or less filter paper to remove any impurities that werelarger than 5 μm. A constant pressure between 5 and 10 PSI wasmaintained on the low pressure cell for the quick filtration of thewaste vegetable oil.

The raw material waste oil was then esterfied to produce alkyl esterproducts and triglycerides. The esterification step was performed bymixing 4.22 g of NaOH per liter of waste vegetable oil with the rawmaterial oil in a container under dry conditions using a magneticstirrer. The mixture was then stirred for six hours using the magneticstirrer to complete the interactions. The total reaction product wasthen left under static conditions overnight to complete thesedimentation of glycerol and sludge at the bottom of the container.During the initial settling phase, if some emulsion was formed due tothe presence of emulsion-forming byproducts in the ester layer, thecontainer was heated to 80° C. or 10 mL of acetic acid per liter of rawmaterial oil was added to the container to break and prevent theemulsion formation.

Next, the alkyl ester products and triglycerides, which were producedduring the esterification step, were separated. To separate theseproducts, after complete sedimentation, the top clear esterified oil wasdecanted slowly and washed for several hours using water while stirringwith a magnetic stirrer. The esterified oil and the washed water whereleft under static conditions overnight to allow for the effectiveseparation of the oil and water phases. The separated oil phase wasdecanted slowly to remove it from the water phase. This process ofwashing was then repeated three times.

Finally, the alkyl ester products were dried. After the final washing,the washed, esterified oil was heated to 80° C. under dynamic conditionsfor 12 hours using a hot plate and a magnetic stirrer to remove waterand methanol further from the alkyl ester products, producing the finalalkyl esters.

Example 3 Production of Fatty Acid Blend

To prepare the fatty acid blend, a solid blend of 28 wt. % of palmiticacid and 72 wt. % of stearic acid was produced. The solid blend was thenheated to 50° C. on a hot plate until the blend was entirely transformedfrom the solid state to the liquid state.

Example 4 Production of Lubricant

The liquid fatty acid blend prepared in Example 3 was mixed with thealkyl esters prepared in Example 2 at a weight ratio of 1:2 before beingheated dynamically. The mixture was stirred with a magnetic stirrerwhile heated to 65° C. on a hot plate. This thermo-mechanical agitationwas continued until the mixture achieved homogenization, producing thelubricant.

Example 5 Production of Sample Drilling Fluid Compositions with AlkylEsters

A sample of each of Drilling Fluids 1-4, as prepared in Example 1, weremixed with alkyl esters as prepared in Example 2. The resulting drillingfluid samples, Samples B 1-B4, included 3 wt. % of the alkyl esters. Thesamples were then tested for coefficient of friction values determinedby a lubricity tester, commercially available as EP and Lubricity Testerfrom OFITE, by loading a portion of each drilling fluid into thelubricity tester and subjecting a test block to 150 inch-pounds oftorque within the sample for 5 minutes. The results for each of thesesamples are provided in Table 3.

TABLE 3 Coefficient of Friction (COF) Values of Samples B1-B4 SampleLubricant Drilling Fluid COF B1 3 wt. % Alkyl Esters Drilling Fluid 10.09 B2 3 wt. % Alkyl Esters Drilling Fluid 2 0.36 B3 3 wt. % AlkylEsters Drilling Fluid 3 0.15 B4 3 wt. % Alkyl Esters Drilling Fluid 40.37

Example 6 Production of Sample Drilling Fluid Compositions withLubricant

A sample of each of Drilling Fluids 1-4, as prepared in Example 1, weremixed with the lubricant as prepared in Example 4. The resultingdrilling fluid samples, Samples C1-C4, included 3 wt. % of thelubricant. The samples were then tested for coefficient of frictionvalues determined by a lubricity tester, commercially available as EPand Lubricity Tester from OFITE, by loading a portion of each drillingfluid into the lubricity tester and subjecting a test block to 150inch-pounds of torque within the sample for 5 minutes. The results foreach of these samples are provided in Table 4.

TABLE 4 Coefficient of Friction (COF) Values of Samples C1-C4 SampleLubricant Drilling Fluid COF C1 3 wt. % Lubricant Drilling Fluid 1 0.03C2 3 wt. % Lubricant Drilling Fluid 2 0.03 C3 3 wt. % Lubricant DrillingFluid 3 0.04 C4 3 wt. % Lubricant Drilling Fluid 4 0.04

Example 7 Production of Sample Drilling Fluid Compositions withCommercially Available Lubricant

A sample of each of Drilling Fluids 1-4, as prepared in Example 1, weremixed with an “ecologically-friendly” lubricant suitable for use indrilling fluids, commercially available as Radiagreen® from Oleon. Theresulting drilling fluid samples, Samples D1-D4, included 3 wt. % of thecommercially available lubricant. The samples were then tested forcoefficient of friction values determined by a lubricity tester,commercially available as EP and Lubricity Tester from OFITE, by loadinga portion of each drilling fluid into the lubricity tester andsubjecting a test block to 150 inch-pounds of torque within the samplefor 5 minutes. The results for each of these samples are provided inTable 5.

TABLE 5 Coefficient of Friction (COF) Values of Samples C1-C4 SampleLubricant Drilling Fluid COF D1 3 wt. % Commercially Drilling Fluid 10.17 Available Lubricant D2 3 wt. % Commercially Drilling Fluid 2 0.11Available Lubricant D3 3 wt. % Commercially Drilling Fluid 3 0.15Available Lubricant D4 3 wt. % Commercially Drilling Fluid 4 0.15Available Lubricant

Example 8 Comparison of Drilling Fluids of Examples 5-7

The results for the samples of Examples 5-7 as well as the baselinecoefficient of friction values of Drilling Fluids 1-4 determined inExample 1 are provided in Table 6.

TABLE 6 Coefficient of Friction (COF) Values of Examples 5-7 SampleLubricant Drilling Fluid COF A1 None Drilling Fluid 1 0.48 A2 DrillingFluid 2 0.38 A3 Drilling Fluid 3 0.20 A4 Drilling Fluid 4 0.39 B1 3 wt.% Alkyl Esters Drilling Fluid 1 0.09 B2 Drilling Fluid 2 0.36 B3Drilling Fluid 3 0.15 B4 Drilling Fluid 4 0.37 C1 3 wt. % LubricantDrilling Fluid 1 0.03 C2 Drilling Fluid 2 0.03 C3 Drilling Fluid 3 0.04C4 Drilling Fluid 4 0.04 D1 3 wt. % Commercially Drilling Fluid 1 0.17D2 Available Lubricant Drilling Fluid 2 0.12 D3 Drilling Fluid 3 0.15 D4Drilling Fluid 4 0.15

As shown by the results provided in Table 6, the inclusion of 3 wt. % ofalkyl esters resulted in a reduction of the coefficient of friction ofDrilling Fluid 1, which contained no monovalent salt or divalent salt.However, this reduction of the coefficient of friction was dramaticallyreduced in Drilling Fluid 3 and negligible in Drilling Fluids 2 and 4.That is, while alkyl esters were an effective lubricant for clay-baseddrilling fluids, such as Drilling Fluid 1, it was ineffective indrilling fluids which contained a monovalent salt or divalent salt.

In contrast, the inclusion of 3 wt. % of the lubricant resulted in abouta 90% reduction of the coefficient of friction of Drilling Fluids 1, 2,and 4 and about a 70% reduction of the coefficient of friction ofDrilling Fluid 3. That is, the disclosed lubricant was an effectivelubricant for both clay-based drilling fluids and drilling fluids whichcontained a monovalent salt or divalent salt. This observation may beattributed to the presence of the fatty acid blend in the lubricant. Asdiscussed previously, the fatty acid blend improves the base lubricatingcapacity of the lubricant. This may be observed in the difference ofcoefficient of friction between Sample B1, which contains alkyl estersbut no fatty acid blend, and Sample C1. Additionally, the fatty acidblend also increases the oxidative stability of the alkyl esters andprevents a loss of lubricating capacity in the presence of monovalent ordivalent salts. This may be observed in the difference of coefficient offriction between Samples B2-B4 and Samples C2-C4.

The commercially available lubricant also displayed a greater reductionof the coefficient of friction of the drilling fluid as compared to thealkyl esters alone. However, the commercially available lubricant onlydisplayed a maximum of about 70% reduction of the coefficient offriction of Drilling Fluids 1, 2, and 4 and about a 45% reduction of thecoefficient of friction of Drilling Fluid 3. That is, commerciallyavailable lubricant was not ineffective in drilling fluids that containa monovalent salt or divalent salt, such as the alkyl esters, but failedto achieve the effectiveness of the disclosed lubricant.

Therefore, based on the results provided in Table 6 and the previousdiscussion, it is evident that a lubricant which comprises both alkylesters and a fatty acid blend of palmitic acid and stearic acid providea greatly increased lubricating capacity and greatly reduced coefficientof friction when compared to similar lubricants.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosure. Since modifications, combinations,sub-combinations and variations of the disclosed embodimentsincorporating the spirit and substance of the disclosure may occur topersons skilled in the art, the scope of the disclosure should beconstrued to include everything within the scope of the appended claimstheir equivalents.

In a first aspect of the present disclosure, a water-based drillingfluid may include a base fluid comprising water, a weighting agent in anamount of from 0.1 wt. % to 75 wt. % relative to the total weight of thewater-based drilling fluid, and a lubricant in an amount of from 1 wt. %to 10 wt. % relative to the total weight of the water-based drillingfluid. The lubricant may include one or more alkyl esters and a fattyacid blend including at least palmitic acid and stearic acid. The sum ofthe weight percent of the palmitic acid and stearic acid may be at least50 wt. % of the fatty acid blend.

A second aspect of the present disclosure may include the first aspectfurther including at least one salt selected from a monovalent salt, adivalent salt, or combinations of these.

A third aspect of the present disclosure may include the second aspectwhere the at least one salt may be present in an amount from 0.01 wt. %to 10 wt. % relative to the total weight of the water-based drillingfluid.

A fourth aspect of the present disclosure may include either of thesecond or third aspects where the at least one salt may be selected fromKCl, NaCl, CaCl₂, or combinations of these.

A fifth aspect of the present disclosure may include any of the firstthrough fourth aspects where the weight ratio of the one or more alkylesters to the fatty acid blend may be from 1:1 to 3:1.

A sixth aspect of the present disclosure may include any of the firstthrough fifth aspects where the molar ratio of palmitic acid to stearicacid may be from 20:80 to 40:60.

A seventh aspect of the present disclosure may include any of the firstthrough sixth aspects where the one or more alkyl esters may be derivedfrom vegetable oil.

In an eight aspect of the present disclosure, a method for making awater-based drilling fluid may include mixing a base fluid, a weightingagent in an amount of from 0.1 wt. % to 75 wt. % relative to the totalweight of the water-based drilling fluid, and a lubricant in an amountof from 1 wt. % to 10 wt. % relative to the total weight of thewater-based drilling fluid. The base fluid may include water. Thelubricant may include one or more alkyl esters and a fatty acid blendincluding at least palmitic acid and stearic acid. The sum of the weightpercent of the palmitic acid and stearic acid may be at least 50 wt. %of the fatty acid blend.

A ninth aspect of the present disclosure may include the eighth aspectwhere the mixing step further includes mixing at least one salt selectedfrom a monovalent salt, a divalent salt, or combinations of these.

A tenth aspect of the present disclosure may include the ninth aspectwhere the at least one salt may be present in an amount from 0.01 wt. %to 10 wt. % relative to the total weight of the water-based drillingfluid.

An eleventh aspect of the present disclosure may include either of theninth or tenth aspects where the at least one salt may be selected fromKCl, NaCl, CaCl₂, or combinations of these.

A twelfth aspect of the present disclosure may include any of the eighththrough eleventh aspects where the molar ratio of the solid palmiticacid to the solid stearic acid may be from 20:80 to 50:50.

A thirteenth aspect of the present disclosure may include any of theeighth through twelfth aspects where the weight ratio of the one or morealkyl esters to the liquid fatty acid blend may be from 1:1 to 3:1.

A fourteenth aspect of the present disclosure may include any of theeighth through thirteenth aspects where the one or more alkyl esters maybe derived from vegetable oil.

A fifteenth aspect of the present disclosure may include any of theeighth through fourteenth aspects further including mixing solidpalmitic acid and solid stearic acid to make a solid fatty acid blend,heating the solid fatty acid blend to form a liquid fatty acid blend,mixing the liquid fatty acid blend with one or more alkyl esters to froma lubricant precursor, and heating the lubricant precursor to atemperature of at least 50° C. and mechanically agitating the lubricantprecursor while heating to form the lubricant.

In a sixteenth aspect of the present disclosure, a method for drilling asubterranean well may include operating a drill in a wellbore in thepresence of a water-based drilling fluid. The water-based drilling fluidmay include a base fluid including water, a weighting agent in an amountof from 0.1 wt. % to 75 wt. % relative to the total weight of thewater-based drilling fluid, and a lubricant in an amount of from 1 wt. %to 10 wt. % relative to the total weight of the water-based drillingfluid. The lubricant may include one or more alkyl esters and a fattyacid blend including at least palmitic acid and stearic acid. The sum ofthe weight percent of the palmitic acid and stearic acid may be at least50 wt. % of the fatty acid blend.

A seventeenth aspect of the present disclosure may include the sixteenthaspect where the water-based drilling fluid further includes at leastone salt selected from a monovalent salt, a divalent salt, orcombinations of these.

An eighteenth aspect of the present disclosure may include theseventeenth aspect where the at least one salt may be present in anamount from 0.01 wt. % to 10 wt. % relative to the total weight of thebase fluid.

A nineteenth aspect of the present disclosure may include either of theseventeenth or eighteenth aspects where the at least one salt may beselected from KCl, NaCl, CaCl₂, or combinations of these.

A twentieth aspect of the present disclosure may include any of thesixteenth through nineteenth aspects where the weight ratio of the oneor more alkyl esters to the fatty acid blend may be from 1:1 to 3:1.

A twenty-first aspect of the present disclosure may include any of thesixteenth through twentieth aspects where the molar ratio of palmiticacid to stearic acid may be from 20:80 to 40:60.

A twenty-second aspect of the present disclosure may include any of thesixteenth through twenty-first aspects where the one or more alkylesters may be derived from vegetable oil.

It should now be understood that various aspects of the compositions andmethods for acid diversion during an acid stimulation treatment of asubterranean formation are described and such aspects may be utilized inconjunction with various other aspects.

It should be understood that any two quantitative values assigned to aproperty may constitute a range of that property, and all combinationsof ranges formed from all stated quantitative values of a given propertyare contemplated in this disclosure. It should be appreciated thatcompositional ranges of a chemical constituent in a composition orformulation should be appreciated as containing, in one or moreembodiments, a mixture of isomers of that constituent. It should beappreciated that the examples supply compositional ranges for variouscompositions, and that the total amount of isomers of a particularchemical composition can constitute a range.

It is noted that one or more of the following claims utilize the term“where” as a transitional phrase. For the purposes of defining thepresent technology, it is noted that this term is introduced in theclaims as an open-ended transitional phrase that is used to introduce arecitation of a series of characteristics of the structure and should beinterpreted in like manner as the more commonly used open-ended preambleterm “comprising.”

Having described the subject matter of the present disclosure in detailand by reference to specific embodiments, it is noted that the variousdetails described in this disclosure should not be taken to imply thatthese details relate to elements that are essential components of thevarious embodiments described in this disclosure, even in cases where aparticular element is illustrated in each of the drawings that accompanythe present description. Rather, the claims appended should be taken asthe sole representation of the breadth of the present disclosure and thecorresponding scope of the various embodiments described in thisdisclosure. Further, it should be apparent to those skilled in the artthat various modifications and variations can be made to the describedembodiments without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various described embodimentsprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A water-based drilling fluid comprising: a basefluid comprising water; a weighting agent in an amount of from 0.1 wt. %to 75 wt. % relative to the total weight of the water-based drillingfluid; and a lubricant in an amount of from 1 wt. % to 10 wt. % relativeto the total weight of the water-based drilling fluid, the lubricantcomprising: one or more alkyl esters; and a fatty acid blend comprisingat least palmitic acid and stearic acid, where the sum of the weightpercent of the palmitic acid and stearic acid is at least 50 wt. % ofthe fatty acid blend.
 2. The water-based drilling fluid of claim 1,further comprising at least one salt selected from a monovalent salt, adivalent salt, or combinations of these.
 3. The water-based drillingfluid of claim 2, where the at least one salt is present in an amountfrom 0.01 wt. % to 10 wt. % relative to the total weight of thewater-based drilling fluid.
 4. The water-based drilling fluid of claim2, where the at least one salt is selected from KCl, NaCl, CaCl₂, orcombinations of these.
 5. The water-based drilling fluid of claim 1,where the weight ratio of the one or more alkyl esters to the fatty acidblend is from 1:1 to 3:1.
 6. The water-based drilling fluid of claim 1,where the molar ratio of palmitic acid to stearic acid is from 20:80 to40:60.
 7. The water-based drilling fluid of claim 1, where the one ormore alkyl esters are derived from vegetable oil.
 8. A method for makinga water-based drilling fluid, the method comprising: mixing a basefluid, a weighting agent in an amount of from 0.1 wt. % to 75 wt. %relative to the total weight of the water-based drilling fluid, and alubricant in an amount of from 1 wt. % to 10 wt. % relative to the totalweight of the water-based drilling fluid, where: the base fluidcomprises water; the lubricant comprises one or more alkyl esters and afatty acid blend comprising at least palmitic acid and stearic acid; andthe sum of the weight percent of the palmitic acid and stearic acid isat least 50 wt. % of the fatty acid blend.
 9. The method of claim 8,where the mixing step further comprises mixing at least one saltselected from a monovalent salt, a divalent salt, or combinations ofthese.
 10. The method of claim 9, where the at least one salt is presentin an amount from 0.01 wt. % to 10 wt. % relative to the total weight ofthe water-based drilling fluid.
 11. The method of claim 9, where the atleast one salt is selected from KCl, NaCl, CaCl₂, or combinations ofthese.
 12. The method of claim 8, where the molar ratio of the solidpalmitic acid to the solid stearic acid is from 20:80 to 50:50.
 13. Themethod of claim 8, where the weight ratio of the one or more alkylesters to the liquid fatty acid blend is from 1:1 to 3:1.
 14. The methodof claim 8, where the one or more alkyl esters are derived fromvegetable oil.
 15. The method of claim 8, further comprising: mixingsolid palmitic acid and solid stearic acid to make a solid fatty acidblend; heating the solid fatty acid blend to form a liquid fatty acidblend; mixing the liquid fatty acid blend with one or more alkyl estersto from a lubricant precursor; and heating the lubricant precursor to atemperature of at least 50° C. and mechanically agitating the lubricantprecursor while heating to form the lubricant.
 16. A method for drillinga subterranean well, the method comprising: operating a drill in awellbore in the presence of a water-based drilling fluid, where thewater-based drilling fluid comprises: a base fluid comprising water; aweighting agent in an amount of from 0.1 wt. % to 75 wt. % relative tothe total weight of the water-based drilling fluid; and a lubricant inan amount of from 1 wt. % to 10 wt. % relative to the total weight ofthe water-based drilling fluid, the lubricant comprising: one or morealkyl esters; and a fatty acid blend comprising at least palmitic acidand stearic acid, where the sum of the weight percent of the palmiticacid and stearic acid is at least 50 wt. % of the fatty acid blend. 17.The method of claim 16, where the water-based drilling fluid furthercomprises at least one salt selected from a monovalent salt, a divalentsalt, or combinations of these.
 18. The method of claim 17, where the atleast one salt is present in an amount from 0.01 wt. % to 10 wt. %relative to the total weight of the base fluid.
 19. The method of claim17, where the at least one salt is selected from KCl, NaCl, CaCl₂, orcombinations of these.
 20. The method of claim 16, where the weightratio of the one or more alkyl esters to the fatty acid blend is from1:1 to 3:1.
 21. The method of claim 16, where the molar ratio ofpalmitic acid to stearic acid is from 20:80 to 40:60.
 22. The method ofclaim 16, where the one or more alkyl esters are derived from vegetableoil.